title: MEG versus EEG localization test using implanted sources in the human brain.
abstract: It is believed that the magnetoencephalogram (MEG) localizes an electrical source in the brain to within several millimeters and is therefore more accurate than electroencephalogram (EEG) localization, reported as 20 mm. To test this belief, the localization accuracy of the MEG and EEG were directly compared. The signal source was a dipole at a known location in the brain; this was made by passing a weak current pulse simulating a neural signal through depth electrodes already implanted in patients for seizure monitoring. First, MEGs and EEGs from this dipole were measured at 16 places on the head. Then, computations were performed on the MEG and EEG data separately to determine the apparent MEG and EEG source locations. Finally, these were compared with the actual source location to determine the MEG and EEG localization errors. Measurements were made of four dipoles in each of three patients. After MEGs with weak signals were discounted, the MEG average error of localization was found to be 8 mm, which was worse than expected. The average EEG error was 10 mm, which was better than expected. These results suggest that the MEG offers no significant advantage over the EEG in localizing a focal source. However, this does not diminish other uses of the MEG.
authors.affiliation: Francis Bitter National Magnet Laboratory, Massachusetts Institute of Technology, Cambridge 02139.
authors.forename: D
authors.initials: D
authors.lastname: Cohen
authors.forename: B N
authors.initials: BN
authors.lastname: Cuffin
authors.forename: K
authors.initials: K
authors.lastname: Yunokuchi
authors.forename: R
authors.initials: R
authors.lastname: Maniewski
authors.forename: C
authors.initials: C
authors.lastname: Purcell
authors.forename: G R
authors.initials: GR
authors.lastname: Cosgrove
authors.forename: J
authors.initials: J
authors.lastname: Ives
authors.forename: J G
authors.initials: JG
authors.lastname: Kennedy
authors.forename: D L
authors.initials: DL
authors.lastname: Schomer
mesh_terms: D000328:Adult; D001921:Brain / Q000502:physiology*; D004567:Electrodes, Implanted; D004569:Electroencephalography; D006801:Humans; D015225:Magnetoencephalography